The present invention relates to medical devices used to differentially ablate or cut deposits from within a patient""s vasculature, and in particular to guide wire braking mechanisms for such medical devices.
A variety of techniques and instruments have been developed for removing health-threatening deposits in a patient""s arteries and similar body passageways. Such deposits may be caused by a number of diseases such as arteriosclerosis, a condition characterized by the buildup of deposits (atheromas) in the intimal layer of a patient""s blood vessels. If the atheroma has hardened into a calcified atherosclerotic plaque, removal of the deposit can be particularly difficult. Deposits in the vasculature can restrict the flow of blood to vital organs, such as the heart or brain, and can cause angina, hypertension, myocardial infarction, strokes, and the like.
Several kinds of atherectomy devices have been developed for removing such deposits. One such device that is particularly suited to removing calcified atherosclerotic plaque, is an ablative rotational atherectomy device, such as that disclosed in U.S. Pat. No. 4,990,134 by Auth. Auth teaches using a small burr covered, or partially covered, with an abrasive cutting material, such as diamond grit. The burr is attached to the distal end of a flexible, rotatable drive shaft. A rotational atherectomy device practicing the Auth invention is sold by the assignee of the present invention under the trademark Rotablator(copyright) and is described below.
The Rotablator(copyright) ablative device 10, depicted in FIG. 1, utilizes a guide wire 26 that is inserted through the patient""s body approximately to the location of the deposit that is to be treated. A hollow, flexible drive shaft 22 having an ablative burr 24 at its distal end is then inserted over the guide wire 26, and advanced to a location just proximal to the deposit. The drive shaft 22 is covered with a lumen or catheter 20 along most of its length to minimize the impact to surrounding tissue when the drive shaft 22 is rotatably engaged. The drive shaft 22 is connected to a compressed-air driven drive assembly 16 having a turbine (not shown) that can rotate the drive shaft 22 at relatively high rotational speeds, typically in the range of, e.g., about 150,000 to about 190,000 rpm. The drive assembly 16 is slidably mounted in an advancer housing 12 on a track 32, allowing a surgeon using the device 10 to move the drive assembly 16 transversely, and hence move the drive shaft 22 and burr 24 forward and backward to ablate the atheroma. When the turbine is engaged, that is, when compressed air is being supplied to the drive assembly 16, a guide wire brake 50 normally clamps onto the guide wire 26, preventing the guide wire 26 from rotating or moving laterally while the drive shaft 22 is rotating.
A prior-art guide wire brake 50 for an ablative rotational atherectomy device is shown in FIG. 2A. This prior art guide wire brake 50 comprises a brake collet 52 axially supported in a brake cylinder 56 containing a free piston 54 with a lip seal 55. The guide wire 26 runs axially through the collet 52, cylinder 56, and piston 54. As seen most clearly in FIG. 2B, the brake collet 52 is an elongate member having an upper portion 41 disposed opposite an identical lower portion 42. The upper and lower portions 41, 42 are separated by a narrow gap 47 along most of the length of the brake collet 52. The brake collet 52 has a tubular back portion 45 and a head portion 46 wherein the head portion 46 upper and lower portions 41, 42 generally form a pair of abutting truncated cones that are coaxial with the back portion 45. The gap 47 separating the upper portion 41 from the lower portion 42 extends entirely through the head portion and most of the way through the back portion 45, wherein interior flat faces 49 on the upper and lower portions 41, 42 are disposed on either side of the gap 47. A narrow strip of the back portion 45 connects the upper portion 41 to the lower portion 42, elastically biasing the upper portion 41 and lower portion 42 in an xe2x80x9cunclampedxe2x80x9d position wherein the gap is wider than the diameter of the guide wire 26.
As shown in FIG. 2A, the piston 54 has a collet engagement orifice 48 that slidably engages the head portion 46 of the collet 52 at the gapped end. Because the head portion 46 is conically tapered, urging the collet engagement orifice 48 axial against the head portion 46 will deflect the upper and lower portions 41, 42 of the collet 52 toward each other, into a closed or clamped position. A spring 53 fits over the brake collet 52 and biases the piston 54 away from the collet 52. During ablation, the compressed air that powers the drive assembly 16 enters the Rotablator(copyright) 10 via a manifold 59 having a first outlet port 61 fluidly connected to the brake cylinder 56, and a second outlet port 62 leading to the drive assembly 16 through tube 30. When compressed air is provided to the drive assembly 16 it is supplied in parallel to the brake cylinder 56. The piston 54 is thereby urged distally toward the brake collet 52, causing the collet engagement orifice 48 to elastically compress the head portion 46 around the guide wire 26 when the turbine is engaged.
Under certain circumstances, it is desirable to override the guide wire brake 50 and release the guide wire 26 even when the turbine and the drive shaft 22 are rotating. For example, it is sometimes desirable to engage the turbine when the drive shaft 22 is advanced over the guide wire 26 to the target position within an artery, or when the drive shaft 22 is being removed from the artery. Sometimes it is also useful to override the guide wire brake to permit advancement or retraction of the guide wire 26 within the rotating drive shaft 22. The Rotablator(copyright) provides a xe2x80x9cdynaglidexe2x80x9d mode wherein the guide wire 26 is enclamped when turbine is operated at a lower velocity in order to facilitate such drive shaft insertion and removal. For these and other situations, a bypass valve 57 is provided between the manifold 59 and the brake cylinder 56, whereby the first manifold outlet 61 to the brake cylinder 56 may be closed. This allows the pressurized gas to drive the turbine without engaging the guide wire brake 50.
An alternative guide wire brake for an atherectomy device is disclosed in U.S. Pat. No. 5,779,722 to Shturman et al., wherein a mechanical guide wire brake is coupled to a mechanical turbine brake. Shturman et al. teaches a mechanical system wherein translation of the turbine along its track, (which is generally performed to move the burr back and forth over the atheroma), has a range of positions that will engage a turbine brake, and a further range that will then release the guide wire brake. A separate override clamp may be secured to the device to release the guide wire brake without engaging the turbine brake. While the device disclosed by Shturman et al. provides an alternate method of ensuring the guide wire brake is engaged when the turbine is operated, the device has the disadvantages of being relatively complicated to build and to operate. In addition, it is possible that the override clamp could be inadvertently left in place, whereby the guide wire could undesirably be free to move.
It is desirable to provide a guide wire brake assembly that ensures that automatically resets any brake override or bypass mechanisms when the drive assembly is engaged. It is further desirable to have a guide wire brake that engages more quickly or earlier than the turbine when the compressed air supply is switched on, and disengages more slowly or later than the turbine, when the compressed air supply is switched off. It is further desirable to provide a guide wire brake that is mechanically simple and easy to operate.
A novel guide wire brake particularly suited to ablative rotational atherectomy devices is disclosed. Ablative rotational atherectomy is a procedure for removing unhealthy deposits within a body by inserting an ablative burr proximate a deposit, and rotating the burr to remove the deposit. A fine guide wire is first inserted, typically through the patient""s vasculature, to the deposit site. A flexible, tubular drive shaft, with the ablative burr at its distal end, is then inserted over the guide wire and guided to the proper location. A catheter covers the drive shaft along most of its length to minimize the impact to local tissues. In normal operation, the guide wire is then clamped at its proximal end to prevent axial or rotational motion, and a prime mover, such as a turbine, is engaged to rotate the drive shaft and burr. The guide wire brake of the present invention clamps the guide wire prior to the activation of the prime mover, and slightly delays the release of the clamp to allow the rotational inertia of the prime mover to dissipate prior to unclamping the guide wire.
In one embodiment the guide wire brake is connected in parallel to a pressurized gas source that drives the prime mover and utilizes a piston in a cylinder to activate the guide wire brake. A pressure relief valve is provided between the pressurized gas source and the prime mover that has an activation pressure greater than the guide wire brake activation pressure, whereby the guide wire brake will engage the guide wire prior to the pressure relief valve opening to the prime mover. Additionally, a check valve is connected to the guide wire brake cylinder that prevents or impedes the flow of gas out of the brake cylinder, thereby delaying the release of the guide wire brake after the pressurized gas source is disconnected or turned off.
In another embodiment of the invention a pneumatic guide wire brake is connected in series between the pressurized gas source and the prime mover. The guide wire brake cylinder includes a side outlet port that leads to the prime mover, whereby the side outlet port does not open until after the guide wire brake has been engaged.
In yet another embodiment of the present invention, a pneumatic guide wire brake is connected in series between the pressurized gas source and the prime mover. The guide wire brake consists of a flexible tube through which the guide wire passes that is suspended within a rigid cylinder. When the pressurized gas passes through the rigid cylinder prior, the increased pressure causes the flexible tube to collapse around the guide wire, thereby clamping the guide wire.
In still another embodiment of the present invention, a mechanically-engaged guide wire brake is provided, wherein rotation of a valve to a first position will engage the guide wire break prior to opening a channel between the pressurized gas source and the prime mover.
In each of the embodiments disclosed herein an optional valve is provided whereby the guide wire brake can be selectively bypassed.